6.5 PRC velocity loss.

[Seabeeken]

The article refers to the moisture content changing as moisture is absorbed and evaporated after its made. Read it or not I dont care, its written by an expert

 

[Seabeeken]

Here is a start. Ill see if I can post the article for you when I return from the range.

 

[BrentM]

2 things mentioned is the validity of the chrono and zero point shift. They are not related. 0 fired to 1x fired brass do generally have different fps and impact points due to the change in the case and tension unless you are very specifically trying to recreate unfired brass spec's. To lose 200 fps you'd be dropping 2-3 grains of powder likely. That is not going to happen with fired vs non fired brass. Moisture content is not even in the mix at this point imho.

Here is what I'd do. Rezero that load with the 1x fired brass. Shoot 500-750 and check drop data. This is the old school method we all used back in the day before labradar and magnetospeed. If you can shoot further without any up/down drafts then go for it. Usually 500-750 area is excellent for feedback without introducing too much vertical from atmospheric.

 

[JAYgs8163]

Borrow someone's Magnettospeed or Labradar and check your velocity.

 

[montanablackdog]

I think best bet is to run the drop data. For that load. Is there online calculator to check that data for my specific load

 

[Seabeeken]

Found this interesting about humidity in powder. 200+ fps speed difference, 10,000 psi pressure difference. You may have seen it before.

 

[308TikkaFan]

Found this interesting about humidity in powder. 200+ fps speed difference, 10,000 psi pressure difference. You may have seen it before.

So thankful I stumbled upon this article… I've been pulling my hair out for ~3 months trying to figure out why my 308 Win accuracy load changed (& loss ~200fps). After this string lightbulb went off realizing my dehumidifier had been off for ~4 months in my basement (70% humidity now), I immediately went straight to the sealed powder bottle (Shooters World S062)… upon loading same weight (scale measures to .01") saw a visible difference in powder volume in the case (~0.2"!!!) AND velocity immediately climbed just shy of 200 fps to the expected accuracy node! Thanks so much y'all!